Adequate nutritional status is a critical determinant of the onset and maintenance of normal reproductive function. It has been established that weight loss causes loss of menstrual function (amenorrhea) and weight gain restores menstrual cycles. Further studies showed that energy balance is more important than body fat mass itself for ovulatory function, since in some cases recovery may occur after minimal reaccquisition of weight, or even long before there is any change in body weight or an increase in body fat.
In both sexes, lower lipid intake and depletion of body lipid reserves can lead to lowered production of sex hormones, in turn impairing reproductive function and fertility.
In women, extreme weight loss can lead to secondary amenorrhea – a cessation of menstrual cycle in a woman that has already menstruated before. This is partly due to lowered production of estrogens, which are necessary for a healthy menstrual cycle, but according to recent scientific studies, the sheer lack of sufficient nutrient intake can negatively affect the menstrual cycle. The presence of amenorrhea means that the patient is most likely not ovulating, a therefore is most likely infertile.
In men, lowered testosterone production can lead to lowered sperm count and quality. If the weight loss progresses into cachexia, subsequent systemic inflammatory activity and oxidative stress further damage the sperm and thus impair reproductive function.